Process for the preparation of 1,4-diamino-2,3-dicyanoanthraquinones

ABSTRACT

There is disclosed a process for the preparation of 1,4-diamino-2,3-dicyanoanthraquinones by reacting compounds of formula ##STR1## wherein X 1  and X 2  are hydroxyl, halogen, acetate or sulfato ester, or, when taken together, are an oxygen atom attached by a double bond to the boron atom, R is a substituent and n is 0, 1 or 2, with an inorganic cyanide in a polar aprotic solvent and in the presence of an oxidizing agent, and subsequently hydrolyzing the reaction product.

The present invention relates to a novel process for the preparation of1,4-diamino-2,3-dicyanoanthraquinones.

A number of processes for the preparation of1,4-diamino-2,3-dicyanoanthraquinone, which is an important intermediatefor dye synthesis, are known in the literature. Thus, for example, aprocess in which 1,4-diaminoanthraquinone, or a derivative thereof whichis substituted in 2- and/or 3-position by chlorine or bromine, isreacted with a cyanide, is disclosed in German Offenlegungsschrift No.25 24 748.

In view of the great importance of 1,4-diamino-2,3-cyanoanthraquinone,this process affords the desired product in too low a yield and purity.

Hence it is the object of the present invention to provide a novelprocess by means of which 1,4-diamino-2,3-dicyanoanthraquinones can beobtained in higher yield and greater purity than heretofore.

It has now been found that the cyanation of the anthraquinone system in2- and 3-position can be carried out in simple manner after converting1,4-diaminoanthraquinones into boron complexes having a1,4-quinonediimine structure.

Accordingly, the present invention relates to a process for thepreparation of 1,4-diamino-2,3-dicyanoanthraquinone, which comprisesreacting a boron complex of formula ##STR2## wherein X₁ and X₂ are eachhydroxyl, halogen, acetate or sulfato ester, or, when taken together,are an oxygen atom attached by a double bond to the boron atom, R is asubstituent and n is 0, 1 or 2, with an inorganic cyanide in a polaraprotic solvent and in the presence of an oxidising agent, hydrolysingthe reaction product so obtained and isolating the resultant1,4-diamino-2,3-dicyanoanthraquinone.

The invention further relates to the novel boron complexes of formula(1), wherein X₁ and X₂ are halogen, to a process for the preparation ofsaid complexes, and to the compounds obtainable by the processes of theinvention.

In the boron complexes of formula (1), X₁ and X₂ are halogen, acetate orsulfate. Preferably X₁ and X₂ are fluorine, chlorine or bromine, withfluorine being particularly preferred.

R may be selected from a great number of substituents that do notinterfere with the process of the invention. Preferred substituents Rare alkyl, alkoxy, --CO₂ alkyl and --CONHalkyl, the alkyl and alkoxymoieties of which preferably contain 1 to 6 carbon atoms. R can also bean acid group such as --SO₃ M and --CO₂ M, wherein M is normallyhydrogen, ammonium or an alkali metal atom, e.g. sodium or potassium.However, R may also be an electronegative group such as nitro, cyano orhalogen, preferably chlorine or bromine.

The boron complexes of formula (1) can contain up to 2 substituents R.Accordingly, n is 0, 1 or 2. Unsubstituted boron complexes (n=0) arenormally most preferred.

The reaction of the boron complexes with inorganic cyanides is carriedout in a polar aprotic solvent. Examples of suitable solvents aredimethylsulfoxide, N,N-dimethylformamide, N-methylformamide,N-methylacetamide, formamide, acetamide, N-methylpyrrolidone,2-pyrrolidone, N-formylmorpholine, N-formylpiperidine, pyridine, ormixtures of such solvents. Preferred solvents are N,N-dimethylformamide,N-methylformamide, 2-pyrrolidone, or mixtures thereof. Especially goodresults are obtained with 2-pyrrolidone.

Suitable inorganic cyanides are sodium, potassium and ammonium cyanide.It is preferred to use sodium cyanide.

The oxidising agent required for the cyanation of this invention isnormally an organic nitro compound, (atmospheric) oxygen,dimethylsulfoxide or sulfur. Preferred contenders from the group oforganic nitro compounds are nitrobenzene, dinitrobenzene andnitrobenzenesulfonic acid, with 3-nitrobenzenesulfonic acid beingparticularly preferred. Suitable oxidising agents are also metal oxidessuch as divanadium pentoxide.

If appropriate, the cyanation can also be carried out in the presence ofammonium salts, e.g. salts of ammonia as well as salts of primary,secondary and/or tertiary amines. Examples of suitable ammonium saltsare ammonium chloride, ammonium sulfate, ammonium phosphate, ammoniumacetate, methylammonium chloride, dimethylammonium chloride,trimethylammonium chloride and tetramethylammonium chloride,ethylammonium chloride, diethylammonium chloride, triethylammoniumchloride and tetraethylammonium chloride, propylammonium chloride,butylammonium chloride, triethylbenzoylammonium chloride, as well as thecorresponding sulfates and phosphates and mixtures of these salts.

The cyanation of this invention can be carried out in a wide temperaturerange. 1,4-Diamino-2,3-dicyanoanthraquinones are obtained in good purityand high yield after the hydrolysis by carrying out the process in thetemperature range from 20° to 100° C., preferably from 60° to 100° C.and, most preferably, from 70° to 90° C.

The hydrolysis following the cyanation is preferably carried out at theboiling point of the reaction mixture. It can be advantageous to carryout the hydrolysis in the presence of a base, e.g. sodium hydroxide orpotassium hydroxide, sodium carbonate or sodium bicarbonate, as aspeeding up of the hydrolysis is often observed under such conditions.

A particularly preferred embodiment of the process of this inventioncomprises reacting a boron complex of formula ##STR3## with sodiumcyanide in 2-pyrrolidone and in the presence of 3-nitrobenzenesulfonicacid at 70° C. to 90° C., and, after addition of water, hydrolysing thereaction product so obtained under reflux.

It has been found advantageous to use, based on the boron complex, a 3-to 6-fold molar excess of organic cyanide, a 1- to 2-fold molar excessof oxidising agent, and a 5- to 10-fold amount (by weight) of solvent.

The 1,4-diamino-2,3-dicyanoanthraquinones are obtained by the abovedescribed process in high yield, usually from 70 to 80%, and in goodpurity, and can be used direct as intermediates for dye synthesis afterbeing washed with e.g. water and without further purifying operations.

The novel boron complexes of formula (1) are prepared by reacting1,4-diaminoanthraquinones with a boron trihalide, or with borontriacetate or boron trisulfate. It is preferred to use a borontrihalide, preferably in the form of an etherate such as (C₂ H₅)₂O.B(Hal)₃. The use of (C₂ H₅)₂ O.BF₃ has proved especially advantageous.

The entire reaction is carried out in the temperature range from 120° to170° C., preferably from 130° to 150° C., in an aromatic organic solventwhich preferably contains halogen atoms, e.g. chlorobenzene,dichlorobenzene or trichlorobenzene. Dichlorobenzene, for example, hasproved particularly suitable.

The boron complexes are obtained in high yield. After washing with thesolvent employed, preferably in conjunction with benzene or toluene,they can be used for the preparation of1,4-diamino-2,3-dicyanoanthraquinones.

The isolation of the boron complexes and of the1,4-diamino-2,3-dicyanoanthraquinones is effected in conventionalmanner, e.g. by suction filtration or centrifugation, and subsequentwashing and drying.

The invention is illustrated by the following non-limitative Examples.

EXAMPLE 1 Preparation of the compound of formula ##STR4##

48 parts by weight of 1,4-diaminoanthraquinone are dissolved in 1000parts by weight of o-dichlorobenzene at 160° C. and 114 parts by weightof boron trifluoride etherate are added. The reaction mixture is stirredfor 10 hours at 140° C. and then filtered hot. The filter residue iswashed with o-dichlorobenzene and toluene and dried.

Yield: 60 parts by weight of the compound of formula (2). The meltingpoint is above 250° C.

    ______________________________________                                        Elemental analysis: C.sub.14 H.sub.8 B.sub.2 F.sub.4 N.sub.2 O.sub.2                 C        H     B         F    N                                        ______________________________________                                        % theory 50,4       2,4   6,5     22,8 8,4                                    % found  50,2       2,5   6,3     22,5 8,4                                    ______________________________________                                    

Carrying out the above procedure with 94 parts of boron trichloride or200 parts of boron tribromide instead of with 114 parts of borontrifluoride etherate affords the corresponding bisboron chloride complexor bisboron bromide complex in comparably good yield.

EXAMPLE 2 Preparation of 1,4-diamino-2,3-dicyanoanthraquinone

A mixture of 41 parts by weight of sodium cyanide, 39 parts by weight of3-nitrobenzenesulfonic acid (sodium salt) and 58 parts by weight of thecompound of formula (2) is added in portions at 80° C. to 400 parts byweight of 2-pyrrolidone. The reaction mixture is stirred for 1 hour at80° C., then diluted with 500 parts by weight of water and refluxed for4 hours. The product precipitates in crystalline form during thishydrolysis. It is isolated hot by filtration, washed with water anddried.

Yield: 44 parts by weight of a product having a purity of 85% (analysisby HPLC), corresponding to a yield of 76%. The melting point is over250° C.

Comparably good results are also obtained by replacing the bisboronfluoride complex of formula (2) by the corresponding bisboron bromide,bisboron acetate and bisboron sulfate complex.

EXAMPLE 3 Preparation of 1,4-diamino-2,3-dicyanoanthraquinone

A mixture of 41 parts by weight of sodium cyanide, 39 parts by weight of3-nitrobenzenesulfonic acid (sodium salt) and 58 parts by weight of thecompound of formula (2) is added in portions at 100° C. to 400 parts byweight of 2-pyrrolidone. The reaction mixture is stirred for 1 hour at100° C., then diluted with 500 parts by weight of water and refluxed for4 hours. The product precipitates in crystalline form during thishydrolysis. It is isolated hot by filtration, washed with water anddried.

Yield: 46 parts by weight of a product having a purity of 80% (analysisby HPLC), corresponding to a yield of 74%. The melting point is over250° C.

Comparably good results are also obtained by using N-methylformamide,N,N-dimethylformamide, dimethylsulfoxide, N-methylacetamide orN-methylpyrrolidone instead of 2-pyrrolidone.

EXAMPLE 4 Preparation of 1,4-diamino-2,3-dicyanoanthraquinone

A mixture of 41 parts by weight of sodium cyanide, 13 parts by weight ofdimethylsulfoxide and 58 parts by weight of the compound of formula (2)is added in portions at 60° C. to 400 parts by weight of 2-pyrrolidone.The reaction mixture is stirred for 4 hours at 60° C., then diluted with500 parts by weight of water and refluxed for 4 hours. The productprecipitates in crystalline form during this hydrolysis. It is isolatedhot by filtration, washed with water and dried.

Yield: 40 parts by weight of a product having a purity of 90% (analysisby HPLC), corresponding to a yield of 73%. The melting point is over250° C.

Comparably good results are obtained by introducing air instead of usingdimethylsulfoxide.

EXAMPLE 5

The procedure of Example 2 is repeated, using 40 parts by weight of1,4-diaminoanthraquinone instead of 58 parts by weight of the compoundof formula (2). No reaction is observed.

What is claimed is:
 1. A process for the preparation of1,4-diamino-2,3-dicyanoanthraquinone, which comprises reacting a boroncomplex of formula ##STR5## wherein X₁ and X₂ are each hydroxyl,halogen, acetate or sulfato ester, or, when taken together, are anoxygen atom attached by a double bond to the boron atom, R is asubstituent and n is 0, 1 or 2, with an inorganic cyanide in a polaraprotic solvent and in the presence of an oxidising agent, hydrolysingthe reaction product so obtained and isolating the resultant1,4-diamino-2,3-dicyanoanthraquinone.
 2. A process according to claim 1,which comprises using a boron complex wherein X₁ and X₂ are fluorine,chlorine or bromine.
 3. A process according to claim 1, which comprisesusing a boron complex wherein R is alkyl, alkoxy, --CO₂ alkyl,--CONHalkyl, --SO₃ M or --CO₂ M, wherein M is hydrogen, ammonium or analkali metal atom, nitro, cyano or halogen.
 4. A process according toclaim 1, wherein the polar aprotic solvent is dimethylsulfoxide,N,N-dimethylformamide, N-methylformamide, N-methylacetamide, formamide,acetamide, N-methylpyrrolidone, 2-pyrrolidone, N-formylmorpholine,N-formylpiperidine, pyridine, or a mixture of such solvents.
 5. Aprocess according to claim 4, wherein the solvent isN,N-dimethylformamide, N-methylformamide, 2-pyrrolidone, or a mixturethereof.
 6. A process according to claim 1, wherein the inorganiccyanide is sodium cyanide, potassium cyanide or ammonium cyanide.
 7. Aprocess according to claim 1, wherein the oxidising agent is an organicnitro compound, oxygen, dimethylsulfoxide, sulfur or divanadiumpentoxide.
 8. A process according to claim 7, wherein the organic nitrocompound is nitrobenzene, dinitrobenzene or 3-nitrobenzenesulfonic acid.9. A process according to claim 1, wherein the cyanation is carried outin the presence of ammonium salts.
 10. A process according to claim 1,wherein the cyanation is carried out in the temperature range from 20°to 100° C.
 11. A process according to claim 1, wherein the cyanation iscarried out in the temperature range from 60° to 100° C.
 12. A processaccording to claim 1, wherein the hydrolysis is carried out at theboiling point of the reaction mixture.
 13. A process according to claim1, which comprises reacting the compound of formula ##STR6## with sodimcyanide in 2-pyrrolidone and in the presence of 3-nitrobenzenesulfonicacid, in the temperature range from 70° to 90° C., and, after additionof water, hydrolysing the reaction product so obtained under reflux. 14.A process according to claim 1, which comprises using, based on theboron complex compound employed, a 3- to 6-fold molar excess ofinorganic cyanide, a 1- to 2-fold molar excess of oxidising agent, andthe 5- to 10-fold amount of solvent.